Acquisition of signals representing a physiological measurement of a living being is important or of interest in many contexts. The signals may be used in clinical settings to provide information for treatment of the living being, but may also be used for general monitoring of a physical condition of the living being. For instance, biopotential acquisition (electrocardiography, electroencephalography, electromyography, etc) and other biological-related measurements (photoplethysmography, bioimpedance, etc) are of interest.
Sensors for contactless measurements may be used for providing higher comfort to a person wearing the sensors, for performing long term recordings, and/or for a reduced set-up time of the sensor.
One problem in acquisition of signals representing a physiological measurement is presence of motion artifacts. In ambulatory measurements, such a problem may be accentuated.
Further, when using contactless measurements, motion artifacts may be especially severe. In contactless measurements, the acquired signal may need to be amplified to a relatively high degree. Also, there may be a relative movement between a contactless sensor and the living being, which may contribute to the motion artifacts. Motion artifacts may thus cause saturation of amplifiers within circuitry used for acquisition and preprocessing of the signal, which prevents any analysis of the signal.
Thus, it would be desired to have a system for acquisition of signals representing physiological measurements, which is more robust to motion artifacts.
In EP 2591720, a biomedical acquisition system with motion artifact reduction is disclosed. The system comprises a digital adaptive filter unit configured to calculate a digital motion artifact estimate, at least one digital-to-analog converter configured to convert the digital motion artifact estimate to an analog signal, and a feedback loop for sending the analog motion artifact estimate signal to a readout channel configured to deduct the analog motion artifact estimate signal from an analog measured ECG signal. However, if noise estimation in this system is not accurate, there is actually a risk of saturating an amplifier by means of the feedback signal.